Aubrey's theory is about rejuvenation, which makes this funnier still. Specifically, he thinks that the world's first 1,000-year-old human has probably already been born. Not through healthy living, improved medicine, cutting infant mortality; all the things that have seen a steady but slow increase in life expectancy. Aubrey thinks we can do it through restoring people on a molecular level to a biologically younger age.

Scary. God, can you imagine if it had happened a generation earlier? Yeah, shut up about the war will you, granddad, you've told us a million times: you were on the beach, getting shot at by the enemy, then King Harold got an arrow right in the eye, blah blah blah . . .

How old is Aubrey, Clare wants to know. He says he's 45. "See, I would have really, thoroughly believed your theory if you had said, 'I'm actually 264 years old'," says the American comedian Reginald D Hunter, who is also on the panel. Well, Reg, he sort of did: he made that joke when he said he was Clare's great-grandfather.

Another comedian, Andy Hamilton, who chairs the panel, says: "Oh, my God, a world full of 800-year-old people – think of the queues at the post office."

"Don't worry," says Aubrey, quick as you like. "There won't be any post offices by then."

The science dude is totally out-funnying the funny guys. At least Andy Hamilton has the good grace to admit it. "Aubrey, that's twice you've been funnier than us," he says. Andy, who has a little beard, is probably feeling out-bearded by Aubrey, too. His really is a thing of wonder, like a big chestnut horse's tail growing out of his face. Maybe that's why they've got Clare on. Mrs de Grey likes to stroke it, he says.

It is a strange idea for a programme: science people putting their theories before a panel of comedians and horse experts who decide whether to pass them or consign them to the shredder of oblivion: Room 101 + 1, kinda. I'm not sure it totally works. But it doesn't really matter, because you get to see cool people like Aubrey de Grey, who clearly should get his own show. His theory is rejected, obviously – because it's a bit scary, a bit bonkers, and the panel feels a bit threatened by him.

They approve the next theory, though, presented by a psychotherapist who says we are in danger of turning sadness into a sickness. She speaks a lot of sense, about how we are fixated with eliminating lows that are perfectly natural and will pass in their own time. And about how we've become a generation of pill-poppers, measuring our lives against false expectation. She's right; you rarely meet a dog that isn't on Prozac these days. She's also not funny, so the panel finally gets a chance to do the jokes.

Which they do well. Especially Reginald D Hunter, who goes off on a long riff about why Hugh Grant is better than Colin Firth. It's not so much what he's saying, more the way he says it, in a beautiful, laconic southern US drawl. I don't know why it's funny; you can't analyse humour too much or it ceases to be funny. All I know is that, right now, on TV, Reginald D Hunter is the person who makes me laugh most. Except Aubrey de Grey and his beard.

I think some of the people in Blitz: The Bombing of Coventry (BBC2) have been at Aubrey's pills. Look at this photo of Alan Hartley, who was a 16-year-old air-raid messenger in 1940. Now he must be 85, but he's got exactly the same expression, the same smile, the same hair even – side parting, Brylcreemed back.

It is extraordinary that this happened in living memory: a whole city turned to rubble overnight by a European neighbour, followed by mass psychosis, a collective nervous breakdown. There was no Prozac back then, so the King went to see the people of Coventry instead, to cheer them up. That did the trick – they buried the dead, rebuilt the city and jolly well got on with it.